Amp swings lower power?

[Cutlass327]

I have 2 amps, a Palomar TX250 and a Shooting Star 225 plus, 10G power cables.

Radio is a Galaxy DX939, lowest output is 2W -> 3W, high is 6W -> 8W using Dosy Test Center.

When key up, DK approx 60W, but audio drops it to 40ish?

Radio is a DX 939, unknown mods but puts out well. Variable power all the way down is around 2W.

Power supply rated at 30A, holds solid 13.8V with everything on and keyed up.

Disconnected the P/S, connected to a battery at a fresh 13.6V charge. It does exactly the same thing on the battery.

I could understand if the DVOM dropped, as ok, meter is 20 years old. But the meter drop AND output drops, that tells me something is wrong.


What am I missing??

 

[midnight special]

what is swr with the amp out of line? what is antenna system set up? coax?jumpers any good?

 

[Cutlass327]

Solarcon A99, 1.2 SWR with and without amp. All jumpers are good that I can tell, as I have moved them around the system in different combinations, including with a dummy load.

 

[Handy Andy]

Do you have a "bench radio" so you can hear your 939 radio while it's running those amps swinging backwards?

IT would be an indication of quality of the audio and RF power.

May be an FM (broadband-spread spectrum) issue - more audio into sidebands and less carrier - makes FM power but looks like it goes down - because there not enough carrier.

The numbers you're getting don't look right, but I'm also not sure of how you measured this and what you used to measure it. So you could be fine, we are just looking at it from a different type of power metering (AVG, RMS and PEP - all are different)

So you really should get out an ammeter and put it in line with the amp to see its' power curve and do it again in line with the 939 so you can see that power curve too.

That way ,you can see the profile and look at where the biggest snag is at and at least you isolated it to either the radio or the amp...

 

[Cutlass327]

I've talked to someone about 17 miles away on just the radio, he'd said it sounded good when I had just got it all hooked up.

I had the Dosy on RMS and Peak, same results.

I have other radios I can hook up, should I just leave no antenna to it, or use dummy or a mag mount mobile antenna on my file cabinet? Talk back on 939 is clear, but I know that is only audio, not RF side.

I had the DVOM ammeter in the amp's line, and it dropped too, I believe over half amp.

 

[Road Squawker]

...edit...

When key up, DK approx 60W, but audio drops it to 40ish?

Power supply rated at 30A, holds solid 13.8V with everything on and keyed up
What am I missing??

Where are you measuring the 13.8vdc? At the PS output terminals or actually at the radio?

Are there any fuses/connections in the powerwire? if so, measure vdc after them under load.
It sounds like the radio isn't getting enuf power.

good luck

 

[Handy Andy]

Ok, then that tells me the Radio is the culprit. Possibly due to AM regulator issues - something in the chain is sapping power when audio gets applied.

That can be from the wrong part used for the AM Regulator - poor Bias - onto a blown cap or poor tune-up.

Some info for the 939 can be found here...
http://www.cbtricks.com/radios/galaxy/dx939/index.htm

 

[Cutlass327]

I measured V at the p/s and at the cord end at the radio. I have a 20A circuit breaker in the amp power line, and checked across the post and ground there, on the aux side of the breaker. That is also where I checked current..

I was told it was tuned up at Bob's in Pa, not sure where that is. Had a sticker on the side "void if removed" with the name on it, but that was gone the first day as I took it open to see if AMC was clipped out or whatever else I could see done.

 

[nomadradio]

If the wattmeter shows the same modulated power with the switch at BOTH peak and average positions, it's defective.

We have encountered a few PDC meters over the years that were missing the part that's connected to the "peak" side of that switch. Can't remember the value, probably 0.22uf or so.

The meter really should read higher on "peak" than it does on average when you modulate the radio.

73

 

[Handy Andy]

I measured V at the p/s and at the cord end at the radio. I have a 20A circuit breaker in the amp power line, and checked across the post and ground there, on the aux side of the breaker. That is also where I checked current..

I was told it was tuned up at Bob's in Pa, not sure where that is. Had a sticker on the side "void if removed" with the name on it, but that was gone the first day as I took it open to see if AMC was clipped out or whatever else I could see done.

I went back to another radio I've worked in several methods and I'm trying to find a board that more closely matches.

There is the problem with a upward spiral of technology getting in the way...the 939 is missing several key areas, you'll have to extrapolate from ones at the site they have information for.

There is the issue of Bipolar, versus MOSFET - you'll see that on the back panel - and it changes the parts count considerably. One earlier generation used Bipolar an all it's support parts then the MOSFET came along and now has added some complexity because even the silkscreen may not show proper diode orientation - they used up and earlier generational board to make the newer upgraded model - so it tells you they are electrically similar - just may not be printed right - which may be the entire problem we're having to deal with here, in the first place.

Perhaps this link may help you locate more of those parts - it's for an older predecessor board but it is for the same layout - its for the 949 - so DON'T PANIC - it is for you to help you...the 939 has a different switch (front panel) layout but the board are nearly the same - identical to the parts used, but some of the layout may not have what your board has.

http://www.cbtricks.com/radios/galaxy/index.htm

The above link is for the purpose of seeing all the site has to offer - not just one but all board types they've got - see if it helps you - I'd personally go to the 949 link - and yes, the Bipolar and MOSFET ones are there - but pay attention to your board number silkscreened on the board for the foil traces and numbering too...all are affected.

On top of that they also have a 959 that has a similar switch and front panel layout as the 939 but it's for SSB and AM modes on top of that all labeled differently - but uses a similar board - go figure?

These are the banes of upstaging to the next platform - THEY use the SAME BOARD, PARTS but the display and switch front panel layouts are different.

But electrically they perform - similar so refer to the 959 for front panel layout but 939 for schematic, 949 can also help for the main PCB layouts, but refer back to the 939 schematic for proper values - ok?

It wouldn't hurt if you opened multiple tabs on your browser and toggled from one to the other to help you find what you need.

(I had to go back and update this so this the best I can offer at the moment)

 

[Cutlass327]

Well, tried my DX88HL. Still drops, with that radio driving it. The 88's display doesn't dim when keyed up though. Maybe 2 issues going on...

 

[Handy Andy]

Ok, had to go over your posts, and re-read them several times.

Let's see if I have this right...

You put an amp inline with the radio - presuming 939 - and it swings backwards...

Now, the other posts you have in here are even more confusing...fo I'm trying to figure out if the backwards swing is from a mod you got with that radio - or you actually have a backwards swing from those amps - and on top of that - you mentioned SHOULD I put this into an antenna or a dummy load - after I started trying to work this all out ... ok ...no big deal but it does add to the mess we have already.

Ok, with the above - the antenna is a REACTIVE problem - and can show backwards swing due to BROADBAND and 2nd harmonic issues - use a dummy load to verify the actual backwards swing - for if it SHOWS FORWARD - on the dummy load, yet backwards on the antenna - there's a problem - the radio or the amp or both. It's producing extra power you're wasting on a harmonic or the input to the amp is not well tuned for the radios' (?) in question.

 

[Cutlass327]

OK, maybe I can help clarify...

Testing is done thru a Dosy Test Center from the mid 90's. There was mention of a cap missing in some, dunno what year ranges that was. I opened it up, and nothing is soldered to the switch but wires, but there is a ckt board in there, haven't tried following anything on it. There is a single ceramic cap on the back of the board.

Dummy load is a MFS 300W bought a month or so ago. There is a single wire wound resistor inside.
--------------------------------------------------------------------------------------------------------------
My connection:
Galaxy 939 -> Palomar TX 250 -> Test Center -> Dummy load

Power for all WAS a 30A power supply, now using car battery fully charged and on a battery tender.

Tried thru dummy load and thru Solarcon A99, same results.

Tried with Galaxy DX88HL, same results.

Using D104 Silver Eagle mic on all tests

CH20 used for tests

--------------------------------------------------------------------------------------------------

939 has unknown mods as I bought it used, had a "Bob's Radio" sticker, from a shop in PA. There is a coil in back by antenna that looks like someone hooked the center and pulled up as they spread it. Ranger EB1 echo has been added. Cannot find evidence of AMC circuit cut.

88HL has been tuned up, low is 2W, high is around 13-15W?? AMC has been put back in by me, tune shop had removed the transistor. Cannot remember the status of filter coils in back. This radio I had bought new, have done a lot of resoldering of bad joints. It has also driven this amp before, long ago in mobile on a Wilson 1000. a Wilson 2000 and another time on dual Antron 1700s. Never noticed "back swing" then.

 

[Handy Andy]

Ok, fantastic!

Thanks this helps...

Then when you turn down power really-really low - like 1 watt - she'll swing forward until is hits a audio level then begin to drop...and drops a lot as audio level goes up?

That signals the amps - and they nay need a little re-work of their inputs - so place the DOSY BEHIND the radio, BUT INTO THE AMPS - and see what SWR shows - you nay need a little tweak, onto, a lot of re-work and possibly rewind a coil or two...

OK, maybe I can help clarify...

Testing is done thru a Dosy Test Center from the mid 90's. There was mention of a cap missing in some, dunno what year ranges that was. I opened it up, and nothing is soldered to the switch but wires, but there is a ckt board in there, haven't tried following anything on it. There is a single ceramic cap on the back of the board.

Dummy load is a MFS 300W bought a month or so ago. There is a single wire wound resistor inside.
--------------------------------------------------------------------------------------------------------------
My connection:
Galaxy 939 -> Palomar TX 250 -> Test Center -> Dummy load

Power for all WAS a 30A power supply, now using car battery fully charged and on a battery tender.

Tried thru dummy load and thru Solarcon A99, same results.

Tried with Galaxy DX88HL, same results.

Using D104 Silver Eagle mic on all tests

CH20 used for tests

--------------------------------------------------------------------------------------------------

939 has unknown mods as I bought it used, had a "Bob's Radio" sticker, from a shop in PA. There is a coil in back by antenna that looks like someone hooked the center and pulled up as they spread it. Ranger EB1 echo has been added. Cannot find evidence of AMC circuit cut.

88HL has been tuned up, low is 2W, high is around 13-15W?? AMC has been put back in by me, tune shop had removed the transistor. Cannot remember the status of filter coils in back. This radio I had bought new, have done a lot of resoldering of bad joints. It has also driven this amp before, long ago in mobile on a Wilson 1000. a Wilson 2000 and another time on dual Antron 1700s. Never noticed "back swing" then.

 

[Cutlass327]

Radio is at 2W on lowest. Key up, no audio, amp output goes to a certain output then drops as soon as audio is put thru mic.

I'll try relocating Dosy later, update what I find. I also have a small Astatic SWR/PWR meter just bought recently to set SWR in my car... I'll compare it too, but I believe it only does 20W max.